Author:

Zhao Deng(Peking University)

Gyrokinetic simulations of L-mode near edge tokamak plasmas with the GYRO code underpredict both the transport and the turbulence levels by 5 to 10 fold [1], which suggest either some important mechanism is missing from current gyrokinetic codes like GYRO or the gyrokinetic approximation itself is breaking down. It is known that GYRO drift-kinetic simulations with gyro-averaging suppressed recover most of the missing transport [2]. With these motivations, we developed a flux tube nonlinear cyclokinetic [3] code rCYCLO with the parallel motion and variation suppressed. rCYCLO dynamically follows the high frequency ion gyro-phase motion (with no averaging) which is nonlinearly coupled into the low frequency drift-waves thereby interrupting and possibly suppressing the gyro-averaging. By comparison with the corresponding gyrokinetic simulations, we can test the conditions for the breakdown of gyrokinetics. rCYCLO nonlinearly couples $\nabla$B driven ion temperature gradient (ITG) modes and collisional fluid electron drift modes to ion cyclotron (IC) modes. As required, rCYCLO cyclokinetic transport recovers gyrokinetics at high relative ion cyclotron frequency ($\Omega^\ast$) and low turbulence levels. However, because the IC modes are stable and act as a turbulence sink, we have found that at high turbulence levels and low-$\Omega^\ast$ cyclokinetic transport is lower (not higher) than gyrokinetic transport. Work is in progress with unstable IC modes to explore the possibility of driving cyclokinetic transport higher than gyrokinetic transport.\par
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[1] C.~Holland, A.E.\ White, et al., Phys.\ Plasmas {\bf 16}, 052301 (2009).\par
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[2] R.E.\ Waltz, Bull.\ Am.\ Phys.\ Soc.\ {\bf 57}, 105 (2012).\par
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[3] R.E.\ Waltz and Zhao Deng, Phys.\ Plasmas {\bf 20}, 012507 (2013).

*Supported by the CSC, NSFC No.\ 1126114032, No.\ 10975012 ITER-CN No.\ 2013GB112006 and the US DOE under DE-FG02-95ER54309.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.NI1.5